1. Field of the Invention
This invention relates to infra-red spectrometers of the multi-wavelength type. More particularly, this invention relates to portable, battery-operated spectrometers used for ambient air analysis.
2. Description of the Prior Art
Portable battery-operated ambient air analyzers have been employed for a number years to determine the concentration of a wide variety of gases and vapors. Such devices typically comprise a hand-held or shoulder-strap-supported housing containing an infra-red source producing a single beam of radiation. This beam is selectively filtered in accordance with the gas to be measured, and is directed through an air sample drawn into a gas cell by an internal sampling pump. The beam emerging from the gas cell is detected by a sensor to produce a signal which is operated on, e.g. by a microprocessor, to develop a concentration measurement for display to the person carrying the analyzer. U.S. Pat. No. 3,877,812 discloses important aspects of one such ambient air analyzer which has been highly successful commercially.
Although such prior art devices have found widespread application, their use has not been permitted in sites such as many kinds of hazardous waste sites which contain potentially inflammable or explosive components. For such more dangerous sites, it has been the usual practice simply to capture an air sample at the site, as in a sealed container, and convey it manually or by vehicle to a remote place for analysis by a non-portable analyzer. Alternatively, for dangerous sites where frequent or continuous monitoring is required, a permanent sampling system may be installed to continuously draw sample gas from the site and transmit it, as through a sealed tube, to an adjacent laboratory for analysis. The analytical equipment used at such laboratory typically will include elaborate isolation provisions and other safety features to prevent damage from explosions or the like of flammable gases which might be drawn in from the site being monitored. Because of such safety provisions, the equipment is necessarily bulky and expensive to manufacture.
It has been found that the prior art techniques for monitoring the air at sites where flammable or explosive mixtures might be present are unsatisfactory, primarily due to high cost and complexity. These difficulties tend to inhibit the monitoring at sites where analysis for toxic gases is very desirable, for example at workplace environments or hazardous waste sites where due to the presence of workers it is vital to know of the existence and the amount of any toxic gases. Thus, it has become very important to provide improved apparatus for monitoring the ambient air at such sites where flammable or explosive gases or vapors may be present.